Near field wireless transmission is increasingly becoming a required feature in a wide variety of consumer goods as well as medical instruments such as for example hearing aids.
In particular in hearing aids inductive coupling is utilised as a wireless transmission means due to minimal power and space available in hearing aids. Therefore miniature coils are incorporated in hearing aids enabling communication either between associated hearing aids or between hearing aids and a remote controller.
German patent no.: DE 198 18 040 discloses a surface mounted device (SMD) coil comprising a duroplastic supporting body with a recess for receiving a flat soldering wire, wherein the flat soldering wire is pressed into the recess ensuring that the flat soldering wire cannot rotate, while leaving a free space allowing slight variations in tolerances.
Further, German patent no.: DE 36 15 037 discloses an SMD coil comprising a ferrite or ceramic supporting body having a length of 3.2 mm. The supporting body has enlarged end pieces with contact plates with recesses for receiving coil wire ends.
The German patents identified above generally describe small inductors to be used in various electronic circuits but not as an antenna. Further, neither of the described inductors is ideal for communication purposes since they are both sensitive to electric field disturbances.
International patent application no.: WO 2005/006491 discloses a loop antenna for receiving data from a non-contact IC-card and attenuating the distant electric field with the attenuation of near magnetic field. The loop antenna has an electromagnetic shield over at least one side of its body, which shield comprises a plurality of electric conductors, a ground contact and a lead wire for connecting the plurality of electric conductors to the ground contact.
However, the loop antenna described in the International patent application is of considerable size. Thus the loop antenna is not suitable for implementation in small sized consumer goods such as a hearing aid. In addition, the shield applied in the loop antenna is complicated to accomplish in fabrication of small and delicate sized antennas.
In addition, International patent application no.: WO 2001/052598 discloses a packaged telecommunication-coil assembly generally referred to as a telecoil, and having a casing shielding the telecoil against radio frequency signals. However, the disclosed casing presents a solution which takes up significant space and thus in hearing aid technology further minimizations are required as well as an improved shielding effect.